Magnetic monopoles have eluded experimental detection since their prediction nearly a century ago by Dirac. Recently it has been shown that classical analogues of these enigmatic particles occur as excitations out of the topological ground state of a model magnetic system, dipolar spin ice. These quasi-particle excitations do not require a modification of Maxwell's equations, but they do interact via Coulombs law and are of magnetic origin. In this paper we present an experimentally measurable signature of monopole dynamics and show that magnetic relaxation measurements in the spin ice material $Dy_{2}Ti_{2}O_{7}$ can be interpreted entirely in terms of the diffusive motion of monopoles in the grand canonical ensemble, constrained by a network of "Dirac strings" filling the quasi-particle vacuum. In a magnetic field the topology of the network prevents charge flow in the steady state, but there is a monopole density gradient near the surface of an open system.
Dynamic scaling near the Kasteleyn transition in spin ice: critical relaxation of monopoles and strings following a field quench
School of Physics and Astronomy, The University of Nottingham（诺丁汉大学物理与天文学学院）；Pitaevskii BEC Center, CNR-INO and Dipartimento di Fisica, Università di Trento（特伦托大学物理系、CNR-INO及皮塔耶夫斯基玻色-爱因斯坦凝聚中心）
我们调查的热输运方冰，自旋冰的二维模拟，探索新兴的磁单极子在输送能量中所发挥的作用。使用基于单自旋翻转动力学的能量保持扩展的动力学蒙特卡罗模拟，我们明确地计算（纵向）热导率，$κ$，在很宽的温度范围内。我们使用两种方法来确定$κ$：在边界处的热浴之间的能量流的测量，和Green-Kubo公式，产生定量一致的热导率值。我们解释这些结果的磁单极子的扩散的能量运输方面。我们涉及的热扩散率，$κ/C$其中$C$是热容量，到一个孤立的扩散常数，表明subdiffusively的扩散系数意味着$κ/C$消失在零温度。最后，我们讨论了这些结果的影响，在三维自旋冰的热输运，在自旋冰材料，如Dy $_2$ Ti $_2$ O $_7$和Ho $_2$ Ti $_2$ O $_7$，并概述了一些悬而未决的问题，在高度挫折磁铁的热输运。
Monopole matter from magnetoelastic coupling in the Ising pyrochlore
烧绿石氧化物晶格上的伊辛模型通常与自旋冰材料和“磁单极子”有关。越来越多的影响连接磁性和弹性自由度的报告，这些和其他相关的挫折材料。在这里，我们扩展了自旋冰哈密顿量，包括自旋和O $^{-2}$离子介导的超交换之间的耦合，我们称之为磁弹性自旋冰模型（MeSI）。人们一直在寻找一个模型，在这个模型中，磁单极子会自发地成为新基态的基石：MeSI哈密顿量就是这样一个模型。尽管它的简单和经典的方法，它描述（自旋和氧晶格）的双层结晶观察Tb $_2$ Ti $_2$ O $_7$。值得注意的是，单单极子的偶极电矩作为磁性的探针出现。作为一个例子，我们表明，在原则上，可以检测到与库仑相位相关的夹点与O $^{-2}$ -离子位移。
